Fillers have been incorporated into interpolymers by melt blending. The preparation of composites by melt blending the polymeric matrix and the filler is a straightforward procedure, but poorly efficient with respect to the properties of the resulting composite. In order to overcome these deficiencies, techniques have been proposed which are based on either the encapsulation of the filler by a polymer coating or the chemical modification of the filler surface. In addition, a polymerization-filling technique has been developed which involves attachment of a Ziegler-Natta-type catalyst onto the surface of an inorganic filler and polymerization of the olefin from the filler surface, (see for example, E. G. Howard et al., Ind. Eng. Chem. Prod. Res. Dev. 20, 421-429 (1981)).
Using this technique, synthesis of polyethylene-based composites by a Al/Ti/Mg catalyst anchored on the surface of kaolin has been reported (International Patent Application WO 96/34900; F. Hindryckx et al., J. Appl. Polym. Sci. 64, 423-438, 439-454 (1997)).
Furthermore, preparation of polymerization-filled composites using a metallocene catalyst has been reported. Kaminsky et al., in German Patent Application DE 3240382, describe the preparation of composites containing polyethylene, or an ethylene butene copolymer, and an inorganic filler using a bis(cyclopentadienyl) zirconocene. Yet, the molar ratios of cocatalyst to catalyst species used in DE 3240382 are very high, ranging from about 32000 to 312500. Synthesis of aluminum- or zinc-containing polyethylene or polypropylene composites has been promoted by a bis(cyclopentadienyl) zirconocene adsorbed on the metal surface (Kaminsky and Zielonka, Polym. Adv. Technol. 4, 415-422 (1993)). Hayashi et al., European Patent Application EP-A-0 374 619, describe polymerization of ethylene in the presence of an organo-aluminum compound and a product obtained by contact treatment of a bis(cyclopentadienyl) zirconocene or a bis(cyclopentadienyl) titanocene catalyst with a filler.
Presently available methods for the preparation of filled composites suffer from various disadvantages. For example, if polymerization does not take place at the filler surface but rather in the homogeneous phase, such as a diluent or solvent, heterogeneous composites are obtained. On the other hand, known methods using polymerization-filling have employed excessive molar ratios of cocatalyst relative to the catalyst species in order to improve polymerization rate and efficiency. A process achieving efficient copolymerization of ethylene or propylene in the presence of a filler with a higher alpha-olefin has not been described yet.
Accordingly, there is a need for an improved process for the preparation of a filled polymer composite, said process eliminating or reducing the disadvantages associated with the known methods and providing a composite with advantageous physico-mechanical properties.
It is the object of the present invention to provide such process.